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We investigate the so-called superWIMP scenario with gravitino as thelightest supersymmetric particle (LSP) in the context of non-standardcosmology, in particular, brane world cosmology. As a candidate of thenext-to-LSP (NLSP), we examine slepton and sneutrino. Brane world cosmologicaleffects dramatically enhance the relic density of the slepton or sneutrinoNLSP, so that the NLSP with mass of order 100 GeV can provide the correctabundance of gravitino dark matter through its decay. We find that with anappropriate five dimensional Planck mass, this scenario can be realizedconsistently with the constraints from Big Bang Nucleosynthesis (BBN) for bothNLSP candidates of slepton and sneutrino. The BBN constraints for slepton NLSPare more stringent than that for sneutrino, as the result, the gravitino mustbe rather warm in the slepton NLSP case. The energy density of gravitinoproduced by thermal scattering is highly suppressed and negligible due to thebrane world cosmological effects.

Gravitino dark matter from increased thermal relic particles